Thiazide-Like Diuretics Attenuate Agonist-Induced Vasoconstriction by Calcium Desensitization Linked to Rho Kinase

Abstract

Abstract-Lowering blood pressure using thiazide-like diuretics, including chlorthalidone and hydrochlorothiazide, has been proven to be effective in clinical studies. However, the mechanisms by which thiazide-like diuretics lower blood pressure are still poorly understood. To evaluate whether thiazide-like diuretics cause calcium desensitization in smooth muscle cells, we measured their effects on agonist-induced increase of blood pressure in Wistar rats in vivo and on agonist-induced vasoconstriction of aortic rings, DNA synthesis, and protein synthesis, RhoA, Rho kinase, and intracellular calcium in vascular smooth muscle cells in vitro. Thiazide-like diuretics significantly attenuated angiotensin II-induced or norepinephrine-induced increase of systolic blood pressure in rats. Thiazide-like diuretics inhibited agonist-induced vasoconstriction of aortic rings in a concentration-dependent manner in the presence and absence of endothelium. The inhibitory effects of thiazide-like diuretics were similar to that of the specific Rho kinase inhibitor Y27632. RT-PCR and immunoblotting showed that RhoA and Rho kinase were significantly reduced in vascular smooth muscle cells after administration of thiazide-like diuretics. In contrast, thiazide-like diuretics did not affect protein tyrosine phosphatase-2 (SHP-2) expression. Agonist-induced changes of intracellular calcium were not affected by thiazide-like diuretics. The study indicates that thiazide-like diuretics inhibit agonist-induced vasoconstriction by calcium desensitization in smooth muscle cells linked to the Rho-Rho kinase pathway. Key Words: diuretics Ⅲ kinase Ⅲ vasoconstriction T hiazide-like diuretics have been the cornerstone in hypertension management for several years. Recent data from the Antihypertensive and Lipid-Lowering to prevent Heart Attack Trial (ALLHAT) showed that blood pressure lowering using thiazidelike diuretics had beneficial effects, including fewer events for all cardiovascular diseases, stroke, and heart failure compared with an angiotensin-converting enzyme inhibitor. 1 Thiazide-like diuretics, including chlorthalidone and hydrochlorothiazide, lower blood pressure by decreasing peripheral resistance rather than by their diuretic effect. 2 Although it has been suggested that thiazide-induced vasodilation is mediated by opening of calcium-activated potassium channels or by inhibition of carbonic anhydrase, 3-5 the precise mechanisms by which thiazide-like diuretics inhibit vasoconstriction and vascular growth are still unclear.Rho is a member of the Ras family of small GTP-binding proteins and cycles between a GDP-bound inactive state and a GTP-bound active state. Rho is involved in regulation of actin/ myosin-dependent contractility in smooth muscle cells. 6 Smooth muscle myosin ATPases are activated after phosphorylation of regulatory myosin light chains by a calcium-calmodulin-dependent myosin light chain kinase, and they are inactivated after dephosphorylation by the calcium-dependent myosin light chain phosphatase. Activation of...

Losartan-hydrochlorothiazide association promotes lasting blood pressure normalization and completely arrests long-term renal injury in the 5/6 ablation model

“…H monotherapy has not been used in the Nx model, although an association of H with hydralazine and reserpine was effective as an antihypertensive (but not renoprotective) regimen (4). In the present study, H provided attenuation of mortality, renal insufficiency, and renal structural injury that was comparable to that obtained with L. This effect involved amelioration of systemic/glomerular hypertension, undoubtedly a result of the diuretic action of H, although a more direct effect is possible (41). However, as with L, inflammation was only marginally attenuated.…”

“…Thus the additional salt-wasting power provided by H may have strengthened the hemodynamic effect of L and allowed its anti-inflammatory action to express fully once the mechanical stretch was removed. This hemodynamic interaction may have been enhanced by a possible vascular effect of H (41). An important additional possibility is that the kaliuretic effect of H greatly alleviated the need for augmented aldosterone production, a view consistent with the low aldosteronemia observed in rats that received LϩH treatment, although a similar result was obtained by L and H monotherapies.…”

“…However, recent clinical studies have shown that H may exert better antihypertensive action (2) and more effective natriuresis (5) than furosemide. The reasons why the beneficial effect of H might equal or even surpass that of furosemide despite its lower natriuretic power are unclear and may relate to the slower H kinetics compared with furosemide, as well as to a possible direct vascular effect (41).…”

Synergism of Hydrochlorothiazide and Nifedipine on Blood Pressure Variability Reduction and Organ Protection in Spontaneously Hypertensive Rats

“…It has been demonstrated that the standard deviation of BP provides an index of overall BPV that is concentrated at low frequencies when studied in the frequency domain, and one major source of slow (or low frequency) hemodynamic perturbations is the myogenic response of vascular smooth muscle cells, which can be attenuated by dihydropyridine calcium channel blockers (27,28). In addition, a recent study proposed that thiazide-like diuretics could inhibit agonist-induced vasoconstriction by calcium desensitization in smooth muscle cells (29). Accordingly, the capacity of nifedipine (a dihydropyridine calcium channel blocker) and hydrochlorothiazide (a thiazide-like diuretic) to attenuate myogenic responses of regional circulations may contribute to their synergistic effects on BPV reduction.…”

Increased Transient Receptor Potential Canonical Type 3 Channels in Vasculature From Hypertensive Rats

“…Animals (SHR and WKY), interventions and hemodynamic measurements, preparation of aortic rings and vasoconstriction, 16,17 culture of VSMC, measurements of cytosolic calcium concentration, 18,19 RNA isolation and RT-PCR, and immunoblottings and immunohistochemistry had been described previously by our group. All experiments were performed as approved by the animal care and use committee.…”